1. Technical Field
The present invention relates generally to an apparatus for crystal growth, and more particularly to a stirring apparatus of an ingot casting furnace.
2. Description of Related Art
An ingot casting furnace is used to produce boules by melting solid materials into liquid state, in which seeds are immersed for crystal growth. A conventional ingot casting furnace includes a crucible, a dome, and a container, wherein the container is hung under the dome to house dopants. Dopants which are vaporized at a high temperature would diffuse into the crucible to be mixed with melted materials to start the process of crystal growth to produce boules, and the produced boules can then be cut to manufacture wafers. However, vaporized dopants tend to accumulate on the upper surface of melted materials, and it is difficult for vaporized dopants to get deeper into melted materials merely by diffusion. Therefore, a boule with uniformly mixed dopants is almost impossible to be produced in this way.
To improve the aforementioned defect, some manufacturers in the industry have proposed to provide a stirring apparatus in the crucible in attempt to uniformly mix dopants in melted materials. Taiwan utility model patent No. M430697 discloses an example of such a stirring apparatus. An ingot casting furnace disclosed in said patent includes a stirring apparatus provided in a crucible, wherein the stirring apparatus is driven by mechanical force to stir materials in the crucible to make vaporized dopants uniformly mixed therein. However, the disclosed stirring apparatus has a plurality of fins installed on the wall of a dome, and such design would increase the difficulty of manufacturing due to the complexity of components. Not only that, in practice, the fins are usually made of quartz, which is a different material from that of the dome, and therefore it is burdensome to work on these two kinds of components to engage them together. Therefore, there is still room for improvements in the design of conventional ingot casting furnaces.